In order to optimize engine performance and reduce undesirable emissions, it is now common to employ an engine control to control various aspects of an internal combustion engine. One method for controlling an engine is to provide an engine control unit with data regarding at least one operation condition of the engine, the control unit utilizing the data to provide an output signal to one or more engine controls.
For example, an oxygen sensor may be employed in the exhaust system of the engine for monitoring the air to fuel ratio. In the event the air to fuel ratio is indicated as too rich (i.e. to much fuel is being supplied in relation to the air), the engine control causes a fuel supply system of the engine to supply less fuel to the engine. In this arrangement, the engine control typically utilizes feedback from the single sensor corresponding to the cylinder which is hottest to make the same adjustment in the air to fuel ratio of the charge supplied to all of the cylinders of the engine.
Several problems have been encountered with this type of engine control. For example, most engines utilize a liquid cooling system which directs coolant along a coolant path through the engine for cooling each cylinder. In this system, the coolant is relatively cool along the beginning of the coolant path near one cylinder, and gets increasingly warm along its path to the end near another cylinder. The first cylinder is thus more effectively cooled than the last cylinder (see FIG. 5).
When fuel is supplied to each of these cylinders, the fuel supplied to the hotter cylinder is more effectively vaporized and less air may enter the cylinder, causing the air to fuel ratio of the charge which is actually delivered to the engine to appear much richer than that of the cooler cylinders. This may occur because data supplied to the engine control indicates that one amount of air is being supplied to the cylinders (such as by a throttle position sensor), but unequal amounts of air actually enter the cylinders because of differences in temperature. When the engine control obtains sensor information indicating that the air and fuel mixture supplied to the hot cylinder is too rich, the engine control sets about reducing the amount of fuel supplied to the cylinders to bring the air to fuel ratio back into the desired range. When this compensation is made (i.e. lessening the amount of fuel supplied to the cylinder by an amount .DELTA.Q) the desired air to fuel ratio is achieved in the hotter cylinder (see FIG. 6(a)). On the other hand, the cooler cylinder(s) already have a leaner air and fuel mixture. The further reduction in fuel amount by the engine control may cause the air and fuel mixture to be too lean, resulting in possible backfiring, stalling or the like (see FIG. 6(b)).
This high engine heat problem may also be experienced when the engine moves from a high speed and/or high load condition to a low load condition. In many engines, the flow rate of coolant through the engine is dependent upon the speed a coolant pump is driven. When an engine is running at high speed, the pump is effective in providing coolant to the engine. If the operator then causes the engine to move to an idle state, the engine remains very hot, but the flow rate of coolant diminishes. The cylinder(s) near the coolant entrance are then cooled much more effectively than those near the end of the coolant flow path (see FIG. 3).
It is, therefore, an object of the present invention to provide an engine control for controlling a combustion condition parameter, such as an air/fuel ratio, when the engine is hot and which overcomes the above-stated problems.